PROJECT SUMMARY/ABSTRACT ? PROJECT 1 Age-related hearing loss (presbyacusis) is a consequence of accumulated environmental stresses to the inner ear and an intrinsic genetically controlled aging process, with as much as 60% of hearing loss in older adults attributable to heritability. The often uncertain medical and noise exposure histories in human subjects coupled with the high variability in the age of onset, rate of progression and the nature and severity of the hearing loss make it difficult to attribute presbyacusis to a specific cause. Moreover, this phenotypic variability and other characteristics strongly suggest that age-related hearing loss is a complex polygenic disorder possibly involving different alleles on multiple genes, although in some instances, it could result from a mutation(s) in a single gene. Advances in next generation sequencing have provided a powerful new tool to address the genetic basis of many age-related diseases. Here we continue to investigate the genetic, molecular and cellular basis of human presbyacusis. Project 1 takes advantage of the Center's extensive and continuously growing database (Core B) containing well documented medical and noise exposure histories and auditory function measures along with DNA samples from large numbers of human subjects. It also capitalizes on the development of new algorithms based on audiograms and data from animal models to define specific age-related hearing loss phenotypes in our subjects. Accordingly, we will perform a comprehensive population-based cohort molecular genetic study to provide information about genetic contributions to specific auditory phenotypes and biological pathways involved with age-related hearing loss. Aim 1.1 continues to identify and validate genetic variants associated with increased susceptibility to presbyacusis by employing molecular genetic analyses using whole exome sequence data from a replication cohort of ?55 year old subjects of non-Finnish European ancestry and an African ancestry cohort. This aim will also investigate causal relationships between specific genetic variants and hearing loss via functional and histopathological analyses of mouse lines generated by knock-in or knock-out of specific candidate genetic variants. Aim 1.2 determines the pathological and potential functional consequences of genetic variants causing age-related hearing loss by assessing the distribution and changes in the expression pattern of promising candidate gene products and their association with pathological changes in human temporal bones.